Light-sensitive device



Aug. 16, 1932. H. A. [ms 1,871,994

' LIGHT SENSITIVE DEVICE- Filed Jan. 1s, 1929 I4 l5 INVENTOR=Harley/910075.

' ATTORNEY Patented Aug. 16, 1932 UNITED STATES PAT NT", OFFICE*IHABLEIY Arms, or WILKINSBURG, PENNSYLVANIA, AssIeNon 'ro WESTINGHQUSEntnc'rnrc a MANUFACTURING COMPANY, A conroaA'rroN or rnNNsYLvANLALIGHT-SENSITIVE DEVICE Application filed January 18, 1929. Serial No.333,470;

My invention relates to light-sensitive devices, and it has particularrelation to the 'utilization of such devices for modulating a carriercurrent 'by means of light variations.

b Substantially all television systems, as at output current from whichis then utilized in the transmission. a

The relatively feeble photo-electric currents are more readily amplifiedif they are made to modulate a carrier wave. At the 7 present time, thiscarrier is most usually supplied by interrupting the beam of lightbefore it reaches the photocell by means of a revolving wheel havingnumerous apertures.

The use of a fluctuating voltage on the photocell to achieve a resultanalogous to the interruption of the light beam has been impractical inthe past by reason of the capacity etween connectingf wires between theelectrodes in the cell,'the percentage of 'modulation being therebyrendered unsatisfactory. It is, accordingly, an object of my inventionto provide a novel combination of a photo-electric cell with circuitnetworks and auxiliary apparatus whereby the cell may be moreefliciently utilized in television and sound-reproduction systems.Another object of my invention is to pro" vide a novel combination of aphoto-electric cell with circuit networks and auxiliary apparatus.whereby a modulated, high-frequency photoelectric current may begenerated."

Another, and more specific, object of my 7 invention is to provide, in anovel combina- 'tion of thetype described, means for supf a pressing acarrier current during non-m0d11- .lating intervals.

.Inpracticing m invention, I interpose a photo-electric cell in onebranch of a circuit network analogous to a Wheatstone bridge,

and associate an output transformer or resistor with that portion of thenetwork which corresponds to the diagonal of the bridge.

A source of oscillations, of any desired frecharacter of theillumination.

By my invention, therefore, I am enabled to prevent overloading of anamplifier associated with the photo-electric cell during nonmodulationintervals, inasmuch as the carrier ing solely determined by the.intensity and frequency is impressed thereon only during such times asthe conductivity of the cell is altered under the influence of light.

The novel features that I consider characterist'ic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, to-

gether with additional applications, objects and advantages thereof,will best be 'understood from the following description of certainspecific embodiments, when read in connection with the accompanyingdrawing, in

which Fig. 1 is a diagrammatic view illustrating" a native form of myinvention which is capable of use in either of the systems shown in Fig.1andinFig.2.

The facsimile-transmitting system illus- 9 trated in Fig. 1 comprises asource l'of modulated carrier-frequency currents, a carrierand aradiating structure, or antenna Inasmuch as the specific manner in whichthe amplifiers and the harmonic generator are frequency amplifier 2, aharmonic producer or frequency changer 3, a power amplifier 4 Iconstructed constitutesno ipeaert n enyelope 8 in which are disposed acathode 10 and an, anode 11, is. positioned within the cylinder. i Y YThe photo-electric cell is so included ina balanced-circuit network asto constitute one:

of the capacitative elementsthereof. The

network preferably comprises an input -in-. ductor 12, which mayor maynot be shunted by a. tuning condenser 13, a resistor 14- and a balancingcondenser 15 connected in the .bridge arm opposite thephotocell, and anoutput reactor 16 and biasing battery 17 connected between anintermed1ate.point on the input inductor and the cathode. The outputinductor may be shunted by a condenser 18,

if desired.

-' A source 20 of carrier-frequency oscilla-- tions is coupled to theinput inductor. The source maybe an oscillation generator of any desiredtype, or it may be constructed and ar- ."In the operation ranged ashereinafter described.

A fixed light source 21 is disposed adjacent to the rotatable cylinder,and a 1ense22 is provided to focus light therefrom to a point upon. thefilm.

scribed, the biasin battery is so adjusted that it is roughly equa tothe peak voltage of the A. C. wave, permitting the voltage on thehotocell to swing from zero to approximatey twice the A. C; peakvoltage. The balancing condenser 15 and balancing resistor 14 are nextso adjusted that no potentials appear across the diagonal of thenetwork, comprising the output reactor and the biasing battery, byreason of A. G. potentials impressed light from the source 21.

across the input inductor. from the oscillator, during such time as thephoto-electric cell is in darkness, or is exposed to the normal amountof light incident thereon, exclusive of When the balance of the networkis disturbed, however, by reason of, variations in resistance of thephotoelectric cell occasioned by variations in the light falling thereonthrough the rotating film,'the carrier frequency will appear in theoutput reactor, modulatedproportionhlly to thelight variations.

It will, accordingly be apparent that, by my invention, I have provideda system whereby the carrier-frequency is preventedfrom causingoverloading of the amplifier phocurrent modulated in accordance with amunity against the detrimental effect of strayof the system debalancingcondenser 15 and the resistor 14,

cathode of thecell and e condenser 15.

on the amplifier stages is strictl propor- (0 'tional to the li htfalling upon t 'e photoelectric cell, an during non-modulatingintervals, the carrier frequency is entirely absent from the couplingreactor and is not impressed at all upon the amplifier. 76

Theap lic'ation of my invention to systems for theelectrical'reproduction of hotographiesound-records isillustrated in 2of the drawing. Such system prefera 1y 1 comprises means 30'-forproducing a carrier- 80 sound-record, a carrier-frequency amplifier 31,a detector and audio-frequency amplifier 32, and a'suitable loud-speakerv33.

The carrier-current producing and modulating portion of the system issubstantially the same as the carrier-current source 1 shown in Fig. 1,conventional means for supporting and advancin a film 34, carrying aphotographic soun record, being substitutedfor the rotating cylinder 6of the facsimile transmitter.

' There are no essential differences in the operation of the twosystems. An additional a vantage'accrues, however, from the use of '6 Emy invention in the re roduction .of sounds photographically recor ed onmotion-picture hns, inasmuch as it provides practical imelectricalpotentials picked up by the am- 1 plifier wiring and by otherconnections. If the carrier frequenc employed is sufliciently high, thecouplingevices in the carrier frequenc amplifier may be so constructedas tobe su stantially opaque to disturbances at audio-frequencies, withthe result th'at the reproduced sound is singularly free from theback-ground noise inevitably present when all the amplification betweenthe photo-elec tric cell and the loud-speaker is at audio-frequencies,asheretofore hasbeen' customary.-

In case it is considered desirable to coup the oscillator to thephoto-electric cell direc 1y, instead of inductively, as shown in Figs.1 and 2, this may readily be accomplished in many difierent wa s. Oneconvenient cou pling network is i Iu'strate'd in Fig. 3 and comprises athermionic tube 40, the grid and plate of which are so. connected toopposite terminals of the input inductor 12 as to constitute the. wellknown shunt-feed Hartly oscillation generator. The photo-electric celland the alancing circuit, comprising the are connected to the inductor12,: as herein.- before described,- and a connection, including thebiasin -battery.17 and an out at resistor 35, exten between an ate pointon the inductor and the 'un'ction between the that I have made a decidedimprovement in 1 the utilization of photo-electric cells in car-'rier-current picture-transmission It will be apparent, from aconsideration of the foregoing description of my invention,

s stems and in systems-for the electrical repro uction of photographicsound records. By reason of the fact that, when using my invention insystems of the types referred to, saturation and overloading of theamplifier stages are obviated, the amplifiers may be materially reducedin capacity, with a consequent saving in material cost and upkeep.

Many other advantages of my invention, as

well as modifications of the specific embodi-' ments thereof chosen forillustration, will at once be obvious to those skilledin the art towhich it pertains. My invention, therefore,

is not to be restricted to theapparatus shown and described, butit is tobe limited in scope only by the prior art and by the spirit of the apended claims;

jclalm as my invention: 1. 'In combination, a 11g 't-sensitive devicehaving an anode and a cathode, a condenser, a resistor and an inputinductor serially connected between said anode and said cathode, anoutput impedance device and a potentialsource extending between one ofsaid electrodes and an intermediate point on said inut inductor, andmeans for impressing oscil- Y atory energy upon saidinput inductor. 2'.In combination, a light-sensitive device l 1 having an anode and acathode, a condenser,

a resistor and an oscillatory input circuit serially connected betweensaid anode and said cathode, an output impedance device and a potentialsource serially connected between one of said electrodes and a point onsaid Input circuit, and means for impressing oscillatory energy uponsaid input circuit.

'3. In combination, a light-sensitive device having an anode and acathode, a condenser, a resistor and an oscillatory input circuitconnected serially between said anode and said cathode, an oscillatoryoutput circuit and a' potential source serially connected between one ofsaid electrodes and a point on said input circuit, means .for impressingoscillatory energy upon said input circuit, and means for derivinglight-modulated energy from said output circuit. a

In testimony whereof; I have hereunto subscriged my name'this 16th dayoi January,

HARLEY A. IIAMS.

